1. Field of the Invention
The present invention relates to improvements in an automatic clutch unit for vehicle use which can be manually operated, too.
2. Related Art
Conventionally, an automatic transmission is well known in which the transmission is automatically controlled in accordance with an engine speed, degree of the accelerator opening and vehicle speed, and a mechanical friction clutch is automatically engaged and disengaged so that the vehicle speed can be controlled. For example, Japanese Examined Utility Model Publication No. 4-8023 discloses an automatic transmission for vehicle use in which the mechanical friction clutch can be manually operated.
According to the automatic transmission disclosed in the above utility model publication, operation is conducted as follows. When a vehicle is started in a specific driving condition, for example, when a vehicle is started while it must get over an obstacle, or when a vehicle is started on a steep slope or a snow-covered road, it is difficult for a friction clutch of the automatic transmission to be appropriately engaged or disengaged, so that it becomes impossible to start the vehicle. In the above case, the automatic clutch control is stopped, and the clutch is manually engaged or disengaged in the automatic transmission disclosed in the above utility model publication. The control system of the above automatic transmission includes: a means for interrupting a clutch operation signal, which is outputted in the changing operation of a gear ratio, when a clutch pedal is depressed; a control valve for controlling the feed of hydraulic fluid to a clutch booster (actuator such as a slave cylinder) in accordance with the motion of the clutch pedal; and a double check valve for selectively feeding the hydraulic fluid to the above booster.
On the other hand, an automatic clutch unit illustrated in FIGS. 3 and 4 is put into practical use, in which the transmission is manually operated and only the clutch is automatically engaged and disengaged in accordance with the operating condition of a vehicle. In the above automatic clutch unit, if necessary, the driver can manually operate the clutch according to his free will when it becomes impossible to operate the clutch automatically.
This automatic clutch unit comprises a manually operated hydraulic fluid feed mechanism 10 and an automatically operated hydraulic fluid feed mechanism 21. The manually operated hydraulic fluid feed mechanism 10 includes: a slave cylinder 4 connected with an upper end of the clutch release fork 3, the lower end of which pushes a release bearing 2, wherein the clutch release fork 3 is turned round a point "a"; a power mechanism 6 operated when a clutch pedal 5 is depressed; a master cylinder 8 having an oil tank 7; and an hydraulic fluid pipeline 9 connected with the cylinder 8. The automatically operated hydraulic fluid -feed mechanism 21 includes: a gear pump 14 connected with an oil tank 11 via a pipeline 12, driven by a motor 13; a hydraulic fluid pipeline 16 connected with the gear pump 14 via a check valve 15; a relief valve 18 arranged in a pipeline 17 from an intermediate portion between the gear pump 14 and the check valve 15, to the oil tank 11; and an electromagnetic valve 20 arranged in a return pipeline 19 provided from the above hydraulic fluid pipeline 16 to the oil tank 11. Both hydraulic fluid pipelines 9 and 16 are connected with a pipeline 23 via a change-over mechanism 22, and the pipeline 23 is connected with the slave cylinder 4.
For example, an electromagnetic change-over valve 22' illustrated in FIG. 4 is used as the change-over mechanism 22. The electromagnetic change-over valve 22' changes over between the hydraulic fluid pipeline 9 of the manually operated hydraulic fluid feed mechanism 10 and the hydraulic pipeline 16 of the automatically operated hydraulic fluid feed mechanism 21, so that hydraulic fluid can be fed into the slave cylinder 4.
In the above arrangement, when the frictional clutch 1 is changed over from the manual to the automatic operation, the change-over mechanism 22 (electromagnetic valve 22') is manually or automatically changed over to the automatic operation. At the same time, when the gear pump 14 is driven by the motor 13, the check valve 15 is opened by the action of pressured hydraulic fluid. Therefore, hydraulic fluid flows into the hydraulic fluid pipeline 16 and the change-over mechanism 22 (electromagnetic valve 22') and then gets into the slave cylinder 4 via the pipeline 23. Therefore, the piston 4a is pushed to the right in FIGS. 3 and 4 by the action of pressured hydraulic fluid. Due to the foregoing, the clutch release fork 3 is turned clockwise around the fulcrum "a", so that the release bearing 2 is pushed to the left, and the friction clutch 1 is disengaged. When a position sensor (not shown in the drawing) arranged in the sleeve cylinder 4 detects that the piston 4a has moved by a predetermined distance, an electric current to be fed to the motor 13 is turned off and the pump 14 is stopped.
After the electric current to be fed to the motor 13 has been turned off and the gear pump 14 has stopped, the electromagnetic valve 20 to adjust a returning speed of hydraulic fluid is opened while its being controlled, hydraulic fluid in the slave cylinder 4 is returned to the oil tank 11 by the returning motion of the piston 4a caused by the spring of the friction clutch 1, the release bearing 2 and the clutch release fork 3, via the pipeline 23, the hydraulic fluid pipeline 16, the return pipeline 19 and the electromagnetic valve 20. Due to the foregoing, the frictional clutch 1 is engaged.
When the change-valve 22 is manually or automatically changed over to the manual operation, the change-over mechanism 22, that is, the electromagnetic change-over valve 22' is changed over to the manual operation side as illustrated in FIG. 4, and then the clutch pedal 5 is depressed. Then the power mechanism 6 is operated, and the piston 8a in the master cylinder 8 is moved to the left in FIGS. 3 and 4. Therefore, hydraulic fluid is sent to the slave cylinder 4 via the hydraulic fluid pipeline 9, the change-over mechanism 22 (electromagnetic change-over valve 22') and the pipeline 23. Accordingly, the piston 4a is pushed to the right in FIGS. 3 and 4. Due to the foregoing, the clutch release fork 3 is turned clockwise round the fulcrum "a", so that the release bearing 2 is pushed to the left. Therefore, the friction clutch 1 is disengaged.
When the clutch pedal 5 is returned to its initial position, the piston 8a in the master cylinder 8 is returned to the right in FIGS. 3 and 4 by the springs in the cylinder 8 and the power mechanism 6. At the same time, by the returning motion of the piston 4a caused by the spring in the friction clutch 1 via the release bearing 2 and the clutch release fork 3, hydraulic fluid in the slave cylinder 4 flows into the pipeline 23 and the hydraulic fluid 9. Then hydraulic fluid returns to the oil tank 7 via the master cylinder 8. Due to the foregoing, the friction clutch 1 is engaged.
In this connection, in the friction clutch operated by hydraulic fluid as illustrated in FIG. 3, when the electromagnetic change-over valve 22' is used for the change-over mechanism as illustrated in FIG. 4, the following problems may be encountered.
(1) Unbalance of quantity of hydraulic fluid between both hydraulic fluid feed mechanisms:
When the above operation to change over between the automatic operation and the manual operation is conducted in the case of engagement of the friction clutch 1, that is when the above operation to change over between the automatic operation and the manual operation is conducted in the case where the piston 4a of the slave cylinder 4 is located at the left end in FIG. 3 so that no hydraulic fluid is accommodated in the slave cylinder 4, no hydraulic fluid flows between both the hydraulic feed mechanisms 10 and 21. Accordingly, no problems are caused. However, when the above operation to change over between the automatic operation and the manual operation is conducted in the case of disengagement of the friction clutch 1, that is, when the above operation to change over between the automatic operation and the manual operation is conducted in the case where the piston 4a of the slave cylinder 4 is located at a position illustrated in FIGS. 3 and 4 or at a right position with respect to the position illustrated in FIGS. 3 and 4 so that the slave cylinder 4 is filled with hydraulic fluid, hydraulic fluid flows between both the hydraulic fluid feed mechanisms 10 and 21. As a result, one of the oil tanks 7 and 11 overflows, and the other is emptied.
For example, after the friction-clutch 1 has been disengaged by depressing the clutch pedal 5, in this case the slave cylinder 4 is filled with hydraulic fluid sent from the oil tank 7, the electromagnetic change-over valve 22' is changed over to the automatic operation. Then the pipeline 23 connected with the slave cylinder 4 is disconnected from the hydraulic fluid pipeline 9 connected with the oil tank, but the pipeline 23 is connected with the returning pipeline 19 of the automatically operated hydraulic fluid feed mechanism 19.
Accordingly, when the electromagnetic valve 20 is opened under the above condition, hydraulic fluid in the slave cylinder 4 flows to the oil tank 11 via the returning pipeline 19, so that the friction clutch 1 can be engaged. The above phenomenon means that hydraulic fluid flows from the oil tank 7 to the oil tank 11. When the above operation is repeated many times, the oil tank 7 is empties as described before, and hydraulic fluid overflows the oil tank 11.
(2) Fast start of a vehicle in the case of a change from automatic operation to manual operation:
When operation is changed over from the automatic operation to the manual operation under the condition that the friction clutch 1 is engaged, no problems are caused. However, when operation is changed over to the manual operation by the electromagnetic change-over valve 22' after the clutch 1 has been disengaged by the automatic operation, the following problems may be encountered. When the clutch pedal 5 is not depressed, the master cylinder 8 and the oil tank 7 are communicated with each other. Accordingly, all hydraulic fluid is returned from the slave cylinder 4 to the oil tank 7 via the pipeline 23, the electromagnetic change-over valve 22' and the hydraulic fluid pipeline 9. As a result, the friction clutch 1 is engaged. Accordingly, there is a possibility that the vehicle starts fast if the gears in the transmission are meshed with each other.
In order to prevent the occurrence of the above problems, it is possible to adopt an alternative arrangement in which the master cylinder 8 is remodeled and the hydraulic fluid passage between the oil tank 7 and the master cylinder 8 is closed under the condition that the clutch pedal 5 is disengaged. However, when the above alternative arrangement is adopted, the following problems may be encountered. For example, after a vehicle has been assembled, air bleeding is conducted so as to bleed air from the pipeline including the slave cylinder 4 and the master cylinder 8. In this case, it is impossible to bleed air that has reached the master cylinder 8.
There is another alternative arrangement in which both oil tanks 7 and 11 are integrated with each other. However, this alternative arrangement is not preferable. The reason is described as follows. In order to conduct air bleeding so as to bleed air from the manually operated hydraulic fluid feed mechanism 10, it is necessary for the oil tank 7 to be located at a position higher than that of the master cylinder 8. In order to prevent the occurrence of problems caused in the clutch when air is mixed in the hydraulic fluid or when the resistance in the pipeline is increased, it is necessary for the oil tank 11 to be located close to the pump 14. Therefore, it is not preferable to integrate both oil tanks 7 and 11.
It is possible to adopt still another alternative arrangement in which the change-over mechanism 22 of the electromagnetic change-over valve 22' is changed over when the clutch is engaged. However, the following problems may be encountered in this case.
(a) A connecting position of the friction clutch is changed when the clutch plate and other parts of the clutch are worn away. Therefore, it is difficult to conduct a positional detection by means of switches.
(b) It is possible to detect the present state of the friction clutch and the operating condition of the vehicle, and the clutch detection point is detected by using an electronic controller in which the results of the above detection is processed. However, when the above arrangement is adopted, the structure becomes complicated. Further, in the case of breakdown of the electronic system, that is, in the case where it is impossible to conduct the automatic operation, the manual operation can not be conducted smoothly.